The invention relates to a fluid actuator device for a high-voltage power circuit breaker with an actuator cylinder having a differential piston and to which pressure medium is applied continuously on the piston end-face of the small area and, selectably applied to the piston end-face of the large area. The fluid actuating device further includes a switching valve to direct pressure medium to the actuator cylinder as well as a mechanical latching device determining the switched-on position of the differential piston.
A device of the type described above is known from Swiss Patent No. 485,313 wherein the smaller piston surface is in free continuous communication with a hydraulic accumulator serving as an energy source without a valve disposed therebetween so that pressure medium is continuously admitted to the piston end-face of the small area. The piston end-face of the large area is selectably acted upon by pressure or relieved of pressure through a switching valve. In this way, a single valve is sufficient. The known breaker actuator is thus maintained in readiness to open by the continuously effective hydraulic accumulator against whose force a mechanical latch acts on the force of the accumulator acting on the switching rod of the electric circuit breaker. The mechanical latch engages the switching rod and holds the actuator piston in the closed position of the breaker.